Common: session renew command

[MikeTheSnowman]

Currently session durations are rather short (only one day). I think it might be a nice feature to have a fcli ssc session renew command that will work in the following way:

• If the user had previously logged in to a session using their user credentials (username/password), then the renew command should just ask the user for a password to generate a new token in order to renew the session.
• If the user had previously logged in to a session using a token, then renew will simply ask for a new token.

[rsenden]

Not sure whether the user name is already being persisted, but doing so would also allow for easier token management commands, where the user just needs to provide the password (reusing both url and user name from the session).